Elevators which are double wound with sheaves on the cab to obtain a 2:1 ratio or larger, will experience rope oscillations when installed for runs which are of long duration
In some cases, the travel of an elevator is as large as 500 to 600 meters as in the cases of tall buildings and dams. In general, lateral oscillation or interference of ropes do not occur when the travel distance is about 150 meters or so. Unfortunately, however, lateral oscillation of the rope inevitably takes place when the travel distance exceeds 150 meters or so. In addition, troubles such as mutual interference of the ropes tends to occur particularly in the case where the ropes are wetted as often experienced in mines. The mutual interference of the ropes may be considerable particularly when the resonance frequency of the rope coincides with the frequency of lateral vibration of the rope, and even rotational oscillation of the cab may occur in the worst case.